The golf ball has a multiplicity of dimples on its surface. The dimples causes turbulence of air flows around the golf ball when flying, thereby creating a turbulent separated flow. This phenomenon is referred to as “creation of turbulence”, and this creation of turbulence shifts backward an air separation point from the golf ball, resulting in reducing drag (force acting in a direction of repulsion against a flying direction). The creation of turbulence increasingly enlarges a deviation between an upper air separation point and a lower air separation point of the golf ball due to a backspin, thereby augmenting a dynamic lift acting on the golf ball. Accordingly, well-designed dimples create better turbulence of the air flows and produce a longer carry.
In recent years, a technology has been also developed to enhance aerodynamic characteristics by polishing the surface of the golf ball in addition to contriving a shape of a dimple. For instance, Patent Document 1 proposes a method for applying a blast treatment over the surface of a coating layer in order to reduce the drag when the golf ball flies. Another instance is that Patent Document 2 proposes a method for applying a rough surface work to a bottom surface of the dimple in order to reduce the drag and improve the dynamic lift when the golf ball flies. Still another instance is that Patent Document 3 proposes a method for forming micro dimples each having a diameter equal to or smaller than ½ as small as a diameter of the dimple formed by the blast treatment in order to extend the carry of the golf ball. Yet another instance is that Patent Document 4 proposes a method for providing roughness to the surface by polishing the surface of the golf ball in order to have an influence on aerodynamic performance of the golf ball.
By the way, a design emphasizing a carry involves adopting a cover having larger hardness as a cover partially configuring a golf ball. On the other hand, not only carry performance but also control performance instanced by producing a desired effect on a spin on, e.g., the green is demanded for being flexible to a variety of scenes during a golf play. Hence, the cover having higher hardness than a general standard is used for the golf ball, in which case the hardness of a coating material forming a coating layer is set softer than the general standard in order to enhance spin performance as the case may be. A softened coating layer is easier to be caught by a face, thereby enabling a spin quantity to be increased on the occasion of an approach shot.